Method and compositions for diffusion patterning

ABSTRACT

Method for patterning organic polymer layers comprising the sequential steps: 
     A. Applying to a substrate an unpatterned layer of acidic polymer dissolved in a plasticizer, 
     B. Applying to the unpatterned layer a second patterned layer which is a liquid solution of organic base dissolved in a volatile solvent; 
     C. Heating the patterned layer to effect removal of the volatile solvent from the layer and diffusion of the second layer plasticizer and organic base into the underlying areas of the acidic polymer layer; and 
     D. Washing the layers with aqueous solution to effect solubilization of the acidic polymer underlying the patterned areas and removal therefrom of the solubilized polymer and plasticizers.

This is a division of application Ser. No. 07/768,504, filed Sep. 30,1991 now U.S. Pat. No. 5,209,814 issued May 11, 1993.

FIELD OF INVENTION

The invention is directed to a method for diffusion patterning oforganic polymer films and to polymeric compositions which are especiallysuitable for patterning by that method.

BACKGROUND OF INVENTION

Thick film technology has historically been an attractive method ofproducing conductors, dielectrics and resistors that are rugged andreliable. The technology is well suited for economical production ofshort production runs. Its ability to be patterned in multilayerconfigurations has allowed fabrication of devices with namely highcircuit density. The successive levels of conductors in the multilayerstructure are separated by insulating dielectric layers and areinterconnected by vias through the dielectric layers.

The multilayer approach is more expensive than a single layer approachbecause it requires painstaking inspection, realignment between thelayers, and careful processing to avoid blistering and cracking.

The most obvious way to reduce these problems associated with multilayerproduction is to reduce line and space dimensions, thereby reducing thenumber of layers in a given structure. The problem with this approachhas been the limited resolution capability of thick film screenprinting, which limits the size of vias used to connect layers ofcircuitry to 10 to 15 mils diameter. Likewise, conductors are limited toa narrowest line width and spacing of 5 to 7 mil lines and spaces inproduction quantities.

Many different approaches have been tried to obtain finer pitch linesand smaller vias. Extremely fine screen mesh and improved emulsionbacking have allowed line resolution of as low as four mils line/spaceto be obtained in limited production. Photoformable pastes have beendeveloped that allow five mil or finer vias, and two to three milline/space pitch. Thick film metallizations have also been patternedwith photoresists and etched to produce fine line patterns and thin filmconductors have been plated up to produce fine line patterns with highconductivity.

All the above approaches have associated drawbacks. For example, finemesh screens typically lay down thinner conductor and dielectric layersthan are desirable. Photoformable pastes have a larger amount of organicmatter that increases shrinkage during firing and can produce dirtyburnout that may render fired parts useless. Conductors produced withphotoformable pastes have an undesirable edge curl that can reduce thereliability of circuits fabricated with them. The processes that requireetch, photoresists or plating are lengthy, process-sensitive andexpensive. Furthermore, some of the processes use solvent that isdifficult to handle. Accordingly, the need continues for a fast,environmentally safe method for making high resolution images in polymerfilms, and particularly in thick films, that avoids the above mentionedproblems.

SUMMARY OF INVENTION

In a first aspect, the invention is directed to a method for making highresolution images on polymer-containing films comprising the sequentialsteps of:

A. Applying to a substrate an unpatterned first layer comprising a soliddispersion of solid acidic organic polymer having an acid number of20-600 in a first plasticizer;

B. Applying to the unpatterned first layer a patterned second layercomprising a liquid solution of organic base and volatile solvent;

C. Heating the patterned second layer to effect removal of the volatilesolvent from the layer and diffusion of the organic base into theunderlying areas of the first layer whereby the acidic polymer in theunderlying areas of the first layer becomes solubilized by reaction withthe organic base; and

D. Washing the layers with aqueous solution having a pH of 5-8.5 toremove the solubilized acidic polymer and plasticizers from thepatterned areas of the layers.

In a second aspect, the invention is directed to a thick film dielectriccomposition for use as the unpatterned first layer in a diffusionpatterning process comprising

A. finely divided particles of inorganic dielectric solids dispersed in

B. a liquid organic medium comprising a solution of

(1) film-forming acidic polymer having an acid number of 20-600,

(2) plasticizer in which the acidic polymer is incompletely soluble; and

(3) volatile organic solvent, the ratio of polymer to plasticizer beingsuch that, when the volatile organic solvent is removed from the organicmedium, the resulting solvent-free polymer/plasticizer dispersion isspecularly nonreflective.

BRIEF DESCRIPTION OF THE DRAWING

The Drawing consists of a single FIGURE which illustrates schematicallythe separate steps of the invention when it is used to pattern a thickfilm paste.

DETAILED DESCRIPTION OF THE INVENTION A. Definitions

As used herein the following terms have the indicated meanings:

The term "eluant" refers to any fluid, either liquid or gaseous, whichis capable of dissolving or otherwise placing the underlying unpatternedlayer into a dispersible form. As applied to the invention, the eluantis aqueous.

The term "dispersible" means with respect to a film of given materialthat the material is capable of displacement or removal by physicaland/or chemical action of a wash liquid. As applied to the invention,the wash liquid is aqueous.

The term "volatile solvent" refers to liquid organic solvents which canbe removed from the unpatterned first layer by heating to 120 C. or lessat atmospheric pressure.

The term "non-crystalline polymer" refers to solid organic polymershaving no more than about 50% crystallinity.

The term "acidic polymer" refers to solid organic polymers having anacid number of 20-600.

The term "solvent free" refers to compositions from which volatilesolvent has been removed substantially completely, i.e. any residualamount of solvent is less than about 1% by weight of the remainingcomposition.

The terms "acrylate" and "acrylic" as used herein to describe monomersand polymers made therefrom include methacrylates as well as acrylates.

All proportions are by weight unless it is otherwise indicated.

B. Detailed Description of the Drawing

The diffusion patterning process can more easily be appreciated byreference to the Drawing, which illustrates schematically the separatesteps of the process as it is applied to the patterning of thick filmdielectric paste.

A layer of thick film dielectric paste 3a is applied by screen printingto alumina substrate 1. The thick film paste is comprised of finelydivided particles of glass dispersed in an organic medium comprising acopolymer of an ethylenically unsaturated carboxylic acid and anacrylate having an acid number of 50 dissolved in dibutyl phthalateplasticizer and terpineol. After printing the layer 3a, the terpineol isremoved by heating the layer to a temperature of 80 C. for a period ofabout 10 minutes.

A patterned second layer 5a is screen printed over the solvent-freethick film layer 3b, the second layer is a viscous liquid comprised ofethyl cellulose binder dissolved in triethanolamine (TEA), dibutylphthalate and terpineol.

Upon forming the patterned layer 5a, the assemblage is heated to 90 C.during which the terpineol is evaporated from the layer and thetriethanolamine and dibutyl phthalate are diffused into the underlyingareas of thick film dielectric layer 3b where the triethanolamine reactswith the acid groups of the polymer to render it water dispersible.

After diffusion is completed, the patterned layer 5b consists mainly ofethyl cellulose and small amounts of residual triethanolamine anddibutyl phthalate. It is then washed with water having a pH of 6 toremove the remaining components of the layer and to remove the solublematerials in the imaged areas of thick film layer 3b. Upon completion ofthe washing, the surface of substrate 1 is exposed in the areas whichunderlay the pattern of layer 3c and a very precise negative image ofthe pattern remains on the surface of substrate 1.

C. Substrate

The method of the invention can be used on either inorganic substrates,such as Al₂ O₃, SiO₂, silicon, AlN and the like, or organic substrates,such as polyimides, phenoxy resins, epoxy resins and the like, orcomposite substrates such as filled organic polymers. When the method ofthe invention is used for making thick film layers, upon completion ofthe washing step, the patterned thick film layer is fired to burn offthe organic constituents of the layer and to effect densification orsintering of the finely divided solid particles.

D. Acidic Polymer

The binder component of the unpatterned first layer, irrespective of themanner in which it is applied, must be film forming, non-crystalline andmust contain a sufficient number of free acid groups that it has an acidnumber of 20-600. So long as the polymer is acidic to that extent, itwill become dispersible when it is exposed to the action of the diffusedorganic basic compound from the patterned layer. While the molecularweight or glass transition temperature (T_(g)) of the polymer is not ofitself critical, it is preferred that the T_(g) be at least 50 C. andpreferably 70 C. or higher in order that less of the polymer can be usedin the layer. Non-crystallinity of the acidic polymer is essential inorder to facilitate diffusion of both the plasticizer and the liquidbase solution from the patterned layer into the thick film layer. Solong as they meet the above three criteria, a wide variety of acidicpolymers can be used as the binder material for the unpatterned firstlayer of the invention.

A primary function of the unpatterned first layer is to serve as adielectric for multilayer electronic circuits. When the dielectriclayers of the multilayer are themselves organic, the polymer itselfserves the dielectric function. But when the layer is a thick film, thepolymer serves as binder for the dielectric solid particles until thelayer is fired.

The purpose of the acid moieties on the polymer molecule is to make theareas of the dielectric layer which underlie the pattern dispersible byreaction with aqueous basic solutions which are diffused into thepolymer from the patterned layer. As mentioned hereinabove, it isnecessary that the number of these acid groups be sufficient to make thepolymer dispersible in water upon exposure to the basic liquid from thepatterned layer. It has been found that an acid number of 20 issufficient for this purpose. However, it is essential that the polymernot be water dispersible before the base reaction. Therefore, the acidnumber of the polymer should not exceed about 600. It is preferred thatthe acidic polymer have an acid number of 100-300.

As will be discussed in more detail hereinbelow, it is essential thatthe acidic polymer be substantially soluble in the plasticizer used inthe unpatterned layer. Nevertheless, it is preferred that the polymernot be soluble in all proportions. Though the method of the inventioncan with difficulty be carried out with an homogeneous polymer layer, itis nevertheless preferred that the polymer be present with theplasticizer as a two-phase system. The interface between the phasesserves as a path which facilitates diffusion of the basic solution fromthe patterned layer and contact with the acidic polymer.

The formation of a two-phase system between the polymer and plasticizerupon solvent removal can easily be observed from the glosscharacteristics of the surface of the resultant polymer/plasticizerfilm. If the film is homogeneous, it will be specularly reflective, i.e.it will have a glossy appearance. On the other hand, if it is in thedesired two-phase state, the film will be specularly non-reflective,i.e. it will have a dull, satin or matte surface. In order properly toobserve specular reflectivity it is necessary to remove any plasticizeror other liquid which may have migrated to the surface.

A wide variety of acid-containing polymers and copolymers can be used inthe invention, such as acrylic polymers, styrene acrylic copolymers,vinyl addition polymers, styrene maleic anhydride copolymers, cellulosederivatives. Likewise, the exact chemical composition of the acid moietyof the acidic polymer is not critical. However, the polymers mostfrequently used will be copolymers of an ethylenically unsaturated acidsuch as acrylic acid, fumaric acid, vinyl sulfonic acid, itaconic acid,methacrylic acid, crotonic acid and the like. The chemical nature of thepolymer backbone is not of itself important so long as the polymer is(1) non-crystalline, (2) film-forming, (3) contains enough acidic groupsso that it will undergo ionization upon exposure to basic solutions, and(4) is capable of forming a two-phase system with the plasticizer in thepatterning layer. Within these criteria, the choice of polymers will bewell within the skill of the known polymer art.

Though it is not necessary to do so, it will be realized that mixturesof acidic and non-acidic polymers can be used as binder for theunpatterned layer if it is desired to obtain special properties nototherwise obtainable from the acidic polymer by itself. However, theacid content of the polymer blend must still be sufficient to render thewhole layer dispersible upon exposure to the diffused base solution. Forexample, it may in some instances be advantageous to use a mixture ofacid-containing polymer with another acid-containing polymer or anon-acid containing polymer which has limited compatibility with thefirst acid-containing polymer to control the phase structure of thepolymer film that is to be patterned. As a result, the base solutionfrom the patterned layer can be more effectively diffused into the lowerlayer to attack the regions that are rich in acid functions and dispersethese regions, thereby causing the film structure to collapse rapidlyand become readily dispersible within the imaged areas.

A few of the many acidic polymers which can be used in the invention arelisted in Table 1 below:

                  TABLE 1                                                         ______________________________________                                        Composition and Properties of Acidic Polymers                                 Composition          Acid No.   M. Wt.                                        ______________________________________                                        Poly(vinyl acetate)   26        30,000                                        Vinyl acetate/crotonic acid copolymer                                                               36        30,000                                        (95/5)                                                                        Cellulose acetate succinate                                                                        136        30,000                                        Ethyl acrylate/methyl methacrylate/                                                                76-85      260,000                                       acrylic acid copolymer (56/37/7)                                              Vinyl acid/crotonic acid/benzophenone                                                               77        50,000                                        copolymer                                                                     Vinyl chloride/vinyl acetate/maleic                                                                 26        --                                            acid copolymer (81/17/2)                                                      Fumaric acid, modified rosin ester                                                                 110-130    --                                            Styrene/maleic anhydride,                                                                          320        50,000                                        partially esterified (50/50)                                                  Styrene/maleic anhydride,                                                                          480         1,600                                        non-esterified (50/50)                                                        Styrene/maleic anhydride,                                                                          350         1,700                                        non-esterified (67/33)                                                        Methyl methacrylate/methacrylic                                                                     59        70,000                                        acid copolymer (92/8)                                                         Methyl methacrylate/ethyl acrylate/                                                                 50        100,000                                       methacrylic acid copolymer (77/15/8)                                          Alkali-soluble thermoplastic resin-                                                                130        --                                            modified aliphatic polyester resin                                            Methyl methacrylate/methacrylic                                                                    119        --                                            acid copolymer (82/7)                                                         Methyl methacrylate/ethyl acrylate/                                                                 80        200,000                                       acrylic acid copolymer (37/56/7)                                              Acrylic acid/alpha methyl styrene/                                                                 197         2,810                                        styrene copolymer                                                             ______________________________________                                    

These acid-containing polymers can be prepared by any of theconventional polymerization techniques known to those skilled in theart, which include solution polymerization, bulk polymerization, beadpolymerization, emulsion polymerization, etc., in the presence of a freeradical generating polymerization initiator, such as peroxy compounds.

E. Plasticizers

Both the unpatterned layer and the patterned layer preferably containsubstantial amount of plasticizers in which the polymer component of theunpatterned layer is at least partially soluble. The primary function ofthe plasticizer in both layers is to facilitate diffusion of the baseliquid from the patterning layer into the underlying areas of theunpatterned layer. While it is not absolutely necessary to haveplasticizer in both layers, it is nevertheless preferred because itgives greater imaging sensitivity. The plasticizers in the two layersmay be the same or different so long as they meet the particularcriteria for the layers. The plasticizer in the lower unpatterned layermust (1) be capable of dissolving the polymer in the unpatterned layer,and (2) preferably capable of forming a solid two-phase system with theacidic polymer in the unpatterned layer. On the other hand, theplasticizer in the patterned layer must be a solvent for the binderpolymer in the patterned layer, for the acidic polymer in theunpatterned layer, and for the organic base.

The amount of plasticizer used in the layers varies widely dependingupon the polymer which is used. As was mentioned hereinabove, it ispreferred to maximize the amount of plasticizer in the unpatterned layerto minimize the amount of polymer which must be burned off when thelayers are thick film pastes. It is preferred that the boiling points ofthe plasticizers be at least 250 C. in order that they remain in thelayer as the volatile solvent is driven off by heating. Nevertheless, itis further preferred that the volatility of the plasticizers be suchthat they can be removed from the system by simple heating if it isdesired to reduce the amount of plasticizer. In fact this technique mayin some instances be preferred since the removal of plasticizer in thismanner leaves holes in the unpatterned film that facilitate diffusion ofplasticizer from the patterned layer.

A wide range of plasticizers can be used to facilitate the penetrationof the base into the polymer film that is to be patterned and to adjustthe film properties. A plasticizer would be selected which showsreasonable compatibility with the binder and other components of thelayers. With acrylic binders, for example, plasticizers can includedibutyl phthalate and other esters of aromatic acids; esters ofaliphatic polyacids such as diisooctyl adipate, and nitrate esters;aromatic or aliphatic acid esters of glycols, polyoxyalkylene glycols,aliphatic polyols; alkyl and aryl phosphates; chlorinated paraffins; andsulfonamide types can be used.

In general, water insoluble plasticizers are preferred for greater highhumidity storage stability and environmental operating latitude, but arenot required. Suitable plasticizers include: triethylene glycol,triethylene glycol diacetate, triethylene glycol diproprionate,triethylene glycol dicaprylate, triethylene glycol dimethyl ether,triethylene glycol bis(2-ethylhexonate), tetraethylene glycoldiheptanoate, poly(ethylene glycol), poly(ethylene glycol) methyl ether,isopropyl naphthalene, diisopropyl naphthalene, poly(propylene glycol),glyceryl tributyrate, diethyl adipate, diethyl sebacate, dibutylsuberate, tributyl phosphate, tris (2-ethylhexyl) phosphate,t-butylphenyl diphenyl phosphate, triacetin, dioctyl phthalate, C₁₂ H₂₅(OCH₂ CH₂)₂ 0OH, tris(2-butoxyethyl) phosphate and phthalates such asdicyclohexyl phthalate, dioctyl phthalate, diphenyl phthalate, diundecylphthalate, butyl benzyl phthalate, 2-ethylhexyl benzyl phthalate.

F. Solids Components

It should be recognized that the method of the invention can be used toimage organic layers alone as well as thick film and other filledlayers. When the method is used for thick films, the solids component ofthe unpatterned layer will generally be a dielectric material, such asglass or a mixture of glass-forming oxides, which will densify and/orsinter when they are fired at, for example, 800-950 C. The chemicalcomposition of the solids is not by itself important with respect toapplication of the invention so long as they are inert to the componentsof the organic medium.

The use of solids in the patterned layer is not always necessary.Nevertheless, the use of finely divided solids is a very useful way ofobtaining appropriate rheological properties of the layer for printingand subsequent processing in accordance with the invention. Thecomposition of the solids in the patterned layer is not otherwiseimportant since they are physically removed from the system by washingafter completion of the diffusion patterning step.

The particle size of the solids is also uncritical. However, it shouldordinarily be in the range of 0.5-20 microns in order to be useful forapplication by screen printing.

G. Patterned Layer Polymer

The primary function of the binder polymer in the patterning layer is toadjust the rheology of the layer consistent with the way it is appliedto the unpatterned layer. Therefore, it is not an essential component ofthe patterned layer in every instance. For example, it is not neededwhen the layer is applied by ink jet printing. However, when thepatterning layer is applied as a thick film paste, the polymer servesboth to adjust the rheology of the paste and as a binder for the finelydivided solids until they are removed in the washing step.

The nature of the binder polymer is not critical within broad limits solong as the rheological properties of the patterning layer areappropriate for the method of application. However, when the patternedlayer is applied as a thick film paste, it is strongly preferred to usecellulosic polymers such as ethyl cellulose as the binder because of itswater solubility and its very desirable thixotropic properties.

H. Organic Base

It is preferred that the basic component of the patterning layer be anorganic base which is compatible with and preferably soluble in theplasticizer. The base can be either liquid or solid. When solid basesare used it is preferred that the melting points not exceed 120 C. Suchmaterials include organic amines such as alkyl amines, aromatic aminessuch as pyridine, morpholine and alkanol amines such as triethanolamine.

The amount of base in the patterning layer must be sufficient to providea solubilizing effect by diffusion into the underlying first layer.

The diffusion patterned areas need to be dispersed with an aqueoussolution in the pH range of 5-8.5. Water is preferred. If necessary, theresulting aqueous solution may contain a low level of a base, preferablythe same base used in the patterning step to help reach the criticalconcentration and make the imaged areas dispersible withoutdeleteriously affecting the unimaged areas. It is preferred that thewash solution pH be at least 5 in order to avoid excessiveneutralization of the diffused base. On the other hand, the pH shouldnot be greater than 8.5 in order to avoid solubilization of non-imagedareas. Optionally, low levels of water soluble surfactants may bepresent in the wash solution to facilitate the interaction between thebase and the acidic polymer film.

I. Formulation and Application

The method of the invention is intended primarily for use as afunctional layer in the fabrication of electronic components. Typicallythe patterned layer which contains dispersibility-changing agent(organic base) will range from 1 to 30 microns thickness while the firstlayer can be of much greater thickness, from 10 to 100 microns. Thethickness of the patterned layer is limited chiefly by the method ofapplication, rather than by considerations of operability.

By and large, the individual steps for preparation of the componentlayers for the method of the invention are similar to those which areknown by those skilled in the art of conventional thick film pastes.

J. Alternative Patterning Methods

It is preferred to carry out the diffusion patterning method of theinvention by screen printing the patterning layer. Nevertheless, thatstep can be carried out by other methods as well. Such methods includethermal transfer, electrophotography, pen plotters and ink jet printing.

Thermal Transfer: The dispersibility changing agents can be formulatedwith polymeric binders and other necessary additives to make a hot meltink composition as practiced by those skilled in the art. The inkcomposition containing the base is precoated on a dimensionally stablethin base, e.g., PET film. The ink ribbon is placed in close contactwith the thick film substrate with the ink facing the thick filmcomposition. Through the base side of the ink ribbon, a thermal headsimilar to those used in commercially available computer printers isused to imagewise affect the transfer of the ink composition into thethick film substrate. If the ribbon formulation and the heatingconditions are adjusted properly, the heat used to generate the patternmay be adequate to affect the diffusion of the active ingredients intothe thick film composition and change its dispersibility behaviorsimultaneously. The element is then processed as previously described.

Alternatively, the patterning can be affected by an IR laser if an IRabsorbing material such as carbon black, graphite or organic dyes whichis very efficient in converting the IR radiation into heat is added tothe formulation. The heat generated in this manner will induce thetransfer of the active ingredients into the thick film substrate.

Typically, the waxy and water-repelling type of binder materials areused in formulating the hot melt inks. If the process is changedslightly, instead of diffusing the ink into the thick film composition,the ink is overprinted on an aqueously developable organic compoundcontaining composition. The water resistant image can be used as a maskor resist for the subsequent aqueous processing for a positive modeoperation.

Electrophotography: The dispersibility changing agents can be formulatedwith polymeric binders, charge directors and adjuvants to make tonerparticles which may be dispersed in a liquid carrier medium as practicedby those skilled in the art. The toner particles are imagewise appliedto the thick film substrate through the various mechanisms that arefamiliar to those skilled in the art. At the fusing step, the activeingredients are driven into the thick film composition to affect thedispersibility change for a predetermined solvent system.

Pen Plotters: The dispersibility changing agents are formulated withadditives in a water- or solvent-based liquid vehicle. The pattern isgenerated with a pen through digital commands as in a commerciallyavailable plotter. The active ingredients are driven into the thick filmcomposition to affect the desired solubility change. The aqueous inksystem is the preferred mode of operation for environmental reasons.

Ink Jet, Liquid Ink: The dispersibility changing agent is formulatedwith additives in a water- or solvent-based liquid vehicle as practicedby those skilled in the art. The images are generated with an ink jetprinthead similar to those found in commercially available computerprinters. The liquid vehicle and/or additives such as plasticizers andsurfactants can be used to carry the active ingredients into the thickfilm composition to effect the solubility change. The use of water-basedink is the preferred mode of operation for environmental reasons.

Ink Jet, Solid Ink: The dispersibility changing agents can be formulatedwith solid vehicle that melts at an elevated temperature. Duringprinting, the ink droplets are ejected in its melted form according tothe digital commands as in those commercially available computerprinters to give high resolution images on the thick film composition.Diffusion of the active ingredients into the thick film compositionchanges the dispersibility in the imaged areas.

The waxy ink composition as often used in this type of application canalso be used as a mask or resist in the same fashion as described in thethermal transfer method for an aqueously developable organic compoundcontaining composition in a positive mode of operation.

The invention will be further illustrated by the following examples:

EXAMPLES EXAMPLE 1

A dielectric thick film element was prepared using the followingcompositions and procedures:

    ______________________________________                                        Dielectric Solids:                                                            Component         % Wt.                                                       ______________________________________                                        Glass A           47.36                                                       Glass B           31.57                                                       Alumina           6.55                                                        Zirconium Silicate                                                                              8.76                                                        Cobalt Aluminate  3.00                                                        Titanium Oxide    2.76                                                        ______________________________________                                    

    ______________________________________                                                        Glass A  Glass B                                              Composition     % Wt.    % Wt.                                                ______________________________________                                        BaO             12.56    11.78                                                SrO             10.82    10.15                                                CaO             6.70     --                                                   ZnO             16.0     21.29                                                Al.sub.2 O.sub.3                                                                              5.50     6.90                                                 SiO.sub.2       46.01    47.64                                                ZeO.sub.2       2.40     2.42                                                 ______________________________________                                    

    ______________________________________                                        Paste Composition:                                                                               Amount                                                     Ingredient         % Wt.                                                      ______________________________________                                        Dielectric Solids  60.0                                                       Elvacite 2010      2.1                                                        Carboset XPD-1234  6.2                                                        Butyl Benzyl Phthalate                                                                           11.2                                                       Tergitol TMN-6     2.1                                                        Terpineol          18.4                                                       ______________________________________                                    

The above paste compositions were prepared in the manner familiar tothose skilled in formulation of thick film materials and were preparedfor printing as follows:

The materials were processed by printing the dielectric optionally one,two or three prints, with each print followed by drying 10 to 15 minutesat 80 to 90 degrees Celsius. A two-phase system was formed upon solventremoval.

    ______________________________________                                        Printing Ink:                                                                                        Amount                                                 Ingredient             % Wt.                                                  ______________________________________                                        Triethanolamine        30                                                     (Fisher Scientific Co., Pittsburg PA)                                         Butyl Carbitol         10                                                     (Aldrich Chem. Co., Milwaukee WI)                                             Deionized Water        60                                                                            100                                                    ______________________________________                                    

The above mentioned components were mixed and stirred to give ahomogeneous solution. The resulting solution was used as printing ink togenerate single dot pattern on the dielectric coating using a HewlettPackard Desk Jet ink jet printer (Hewlett Packard, Palo Alto, Calif.).The imaged element was baked at 75 C in an oven for 5 min. It was thenimmersed in warm water at 60 C. with ultrasonic agitation for 1 min. 130micron wide and 26 micron deep vias with perfectly round shape andstraight walls were obtained.

EXAMPLE 2

A printing ink was prepared using the following procedure:

    ______________________________________                                        Printing Ink:                                                                                        Amount                                                 Ingredient             % Wt.                                                  ______________________________________                                        Triethanolamine        30                                                     (Fisher Scientific Co., Pittsburg PA)                                         Merpol SH              1.0                                                    (E. I. du Pont Co., Wilmington DE)                                            Deionized Water        69                                                                            100                                                    ______________________________________                                    

The above mentioned components were mixed and stirred to give ahomogeneous solution. The resulting solution was used as printing ink togenerate a single dot pattern on the dielectric thick film described inExample 1. The imaged element was baked at 75 C. in an oven for 5minutes. It was then immersed in warm water at 60 C. with ultrasonicagitation for 1 minute. 130 micron wide and 24 micron deep vias withperfectly round shape and good edge definition were obtained.

EXAMPLE 3

A dielectric thick coating was prepared using the following procedure:

    ______________________________________                                                              Amount                                                  Ingredient            % Wt.                                                   ______________________________________                                        Dielectric Solids (as in Example 1)                                                                 58.25                                                   Elvacite 2051         1.01                                                    Carboset XPD-1234     9.08                                                    Butyl Benzyl Phthalate                                                                              16.51                                                   Terpineol             15.13                                                                         100.0                                                   ______________________________________                                    

The above mentioned paste composition was prepared and printed on thealumina substrate as described in Example 1.

A printing ink was prepared using the following procedure:

    ______________________________________                                                               Amount                                                 Ingredient             % Wt.                                                  ______________________________________                                        Triethanolamine        30                                                     (Fisher Scientific Co., Pittsburg PA)                                         Acetic Acid            6.7                                                    (EM Science, Gibbstown NJ)                                                    Deionized Water        63.3                                                                          100                                                    ______________________________________                                    

Triethanolamine was dissolved in deionized water. Acetic acid was slowlyadded with agitation. The resulting solution having a pH of 8.5 was usedas printing ink to generate the single dot pattern on the dielectricthick film using a Hewlett Packard DeskJet printer (Hewlett Packard,Palo Alto Calif.). The imaged element was heated from the back side atabout 200 C. for 3 sec on, followed by baking at 75 C. in an oven for 5min. It was then immersed in warm water at 60 C. with ultrasonicagitation for 1 min. 160 micron wide and 29 micron deep vias with veryround shape and sharp definition were obtained.

EXAMPLE 4

Dielectric paste and patterning paste having the following compositionswere screen printed on the substrate described in Example 1 usingtechniques known to one skilled in the art.

The dielectric vehicle had the following composition:

    ______________________________________                                                              Amount                                                  Ingredient            % Wt.                                                   ______________________________________                                        Poly(methyl methacrylate)                                                                            2                                                      Methyl Methacrylate/Methacrylic                                                                     18                                                      Acid Copolymer                                                                Butyl Benzyl Phthalate                                                                              42                                                      Terpineol             38                                                      ______________________________________                                    

The dielectric paste had the following composition:

    ______________________________________                                                           Amount                                                     Ingredient         % Wt.                                                      ______________________________________                                        Inorganic Solids   64                                                         Dielectric Paste Vehicle                                                                         36                                                         ______________________________________                                    

The patterning paste vehicle had the following composition:

    ______________________________________                                                           Amount                                                     Ingredient         % Wt.                                                      ______________________________________                                        Ethyl Cellulose     4                                                         Triethanolamine    42                                                         Terpineol          27                                                         Butyl Benzyl Phthalate                                                                           27                                                         ______________________________________                                    

The patterning paste had the following composition:

    ______________________________________                                                           Amount                                                     Ingredient         % Wt.                                                      ______________________________________                                        0.45 Micron Alumina                                                                              63.5                                                       Patterning Paste Vehicle                                                                         38.5                                                       ______________________________________                                    

The patterning layer was then printed by using a via fill screen withseveral sizes of via openings. The patterning paste was then dried at 80to 100 C. for 5 to 10 min. Uniform, well defined vias with steep sidewalls were produced. Average size was 4-5 mils, dielectric filmthickness was in excess of 30 microns.

GLOSSARY

Carbitol: Trademark of Union Carbide Corp., Danbury, Conn. fordiethylene glycol ethyl ethers.

Carboset XPD-1234: Trademark of B. F. Goodrich & Co., Cleveland, Ohiofor acidic methylmethacrylate copolymers.

Elvacite 2051: Trademark of E. I. du Pont de Nemours and Co.,Wilmington, Del. for methyl methacrylate resins.

Merpol SH: Trademark of E. I. du Pont de Nemours and Co., Wilmington,Del. for non-ionic esters of ethylene oxide.

Santicizer S-160: Trademark of Monsanto Chemical Co., St. Louis, Mo.,for N-alkyl-paratoluenesulfonamide plasticizers.

Tergitol TMN-6: Trademark of Union Carbide Corp., Danbury, Conn. fornon-ionic surfactants.

We claim:
 1. A composition for use as the first unpatterned layer in adiffusion patterning process comprising finely divided particles ofinorganic dielectric solids dispersed in a liquid organic mediumcomprising a solution of a film-forming acidic polymer having an acidnumber of 20-600; a plasticizer in which the acidic polymer isincompletely soluble; and a volatile organic solvent wherein the ratioof polymer to plasticizer being such that when the volatile organicsolvent is removed from the organic medium, the resulting solvent-freepolymer/plasticizer dispersion is specularly nonreflective.
 2. Thecomposition of claim 1 in which the acidic polymer comprises a minoramount by weight of the solvent-free organic medium.
 3. The compositionof claim 1 in which the acidic polymer has an acid number of 100-400. 4.The composition of claim 1 in which the acidic polymer is a copolymer ofan hydrocarbyl acrylate or methacrylate with an ethylenicallyunsaturated carboxylic acid.
 5. The composition of claim 1 in which theplasticizer is water-insoluble.
 6. The composition of claim 1 in whichthe plasticizer is a glycol.